Management of momentum and attitude steering utilizing flywheels in spacecraft is known today. Such spacecraft often employ momentum bias and wheel gimbaling to accomplish momentum management and attitude steering.
Energy storage utilizing electrochemical battery technology is also well established in the art. Although alternative energy storage strategies, such as those employing flywheels, have been explored, the achievable energy densities did not surpass the energy densities of electrochemical batteries.
The recent development of suitable materials has enabled improvements in achievable energy densities of flywheel systems by permitting higher rotational speeds. Current flywheel systems may have rotational speeds exceeding 100,000 RPM. These operating speeds require a non-contacting bearing system, such as a magnetic suspension system, to overcome frictional losses and mechanical wear. As is known in the art, successful magnetic suspension systems require sophisticated control strategies and equipment to mollify the effects of disturbances to the system. Recent advancements in microprocessor operating speeds have enabled control of magnetic suspension systems which can successfully accommodate the higher operating speeds necessary for these applications. Thus, energy storage in spacecraft utilizing flywheels is now feasible.
Unlike electrochemical energy storage systems, energy storage and retrieval utilizing a flywheel system affects the attitude steering and momentum control of the spacecraft. Therefore, it is desirable to integrate the control of attitude steering and momentum management with the control of energy storage in the flywheel system of the spacecraft.
A combined energy storage attitude control, and attitude reference system is disclosed in U.S. Pat. No. 4,723,735 to Eisenhaure et al. The system disclosed by Eisenhaure utilizes counter-rotating flywheels for attitude steering and energy storage in a zero-momentum spacecraft. That design would not be appropriate for use with momentum-bias spacecraft, however. Furthermore, the momentum change and associated torques available for attitude steering, utilizing counter-rotating flywheels, is approximately one-half that available for similarly sized flywheels which rotate in the same direction.